DHCPOFFER packets blocked towards guest Wifi

I have created a guest Wifi on my Omnia and configured DHCP for it. I also added a firewall rule to allow UDP traffic from any host in this network to ports 67 to 68 on the router.

I do actually see DHCPDISCOVER messages in /var/log/messages but somehow the replies don’t get through:

2018-06-23T21:07:21+02:00 info dnsmasq-dhcp[20371]: DHCPDISCOVER(wlan1-1) 78:11:dc:7e:10:87 
2018-06-23T21:07:21+02:00 info dnsmasq-dhcp[20371]: DHCPOFFER(wlan1-1) 78:11:dc:7e:10:87 
2018-06-23T21:07:21+02:00 warning dnsmasq-dhcp[20371]: Error sending DHCP packet to Operation not permitted

Am I missing something obvious? I’m not aware of anything I have done that could cause this. Where would I start looking?

Thanks in advance for any help!

Easiest way is to enable guest in Foris directly by one click.
Otherwise UTFG or go directly to https://wiki.openwrt.org/doc/recipes/guest-wlan-webinterface.
From your post is not clear what you did or didn’t already so it is hard to help.

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Thanks for looking into this! Comparing my setup to the linked instructions, it was indeed quiet similar. The difference is that I had a Firewall rule for Guest->WAN that has “output” set to “disallow”. Changing that to “allow” fixes my issue.

I don’t quite understand what a rule for traffic between the guest network and the WAN has to do with traffic from the router to the guest network. Can anybody explain that to me? I’d really like to keep that rule as it was.